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Daryoush Khorramian , Soroush Sistani , Amin Banaei , Salar Bijari ,
Volume 75, Issue 7 (October 2017)
Abstract

Background: There are several techniques for reducing the delivered dose from CT (Computed tomography) scanning such as the automatic exposure control (AEC). This technique modulates the tube current regarding the patient size and weight. The aim of this study was to estimate the effect of the AEC on the radiosensitive organs effective doses in women undergoing chest CT scanning.
Methods: This study was a cross-sectional, analytical and quantitative study that was performed during 3 months in the imaging section of the Firoozgar educational and therapeutic hospital (belonging to Shahid Beheshti University of Medical Sciences) in the spring of 2017. CT scan exposure parameters were gathered and registered for 54 women undergoing chest CT scan. 25 of these scans were performed using AEC system and 29 of them were performed without using AEC. CT dose indexes in the center and peripheral regions of the standard phantom were calculated using the exposure parameters. Weighted CT dose index was also calculated and effective organ doses were obtained using CT-Expo software, version 2 (Medizinische Hochschule, Hannover, Germany) for two mentioned groups. In addition, noise was measured for these two groups as an image quality parameter.
Results: Calculated weighted CT dose indexes were 9.94 mGy and 12.46 mGy using AEC system and without using AEC, respectively. The calculated effective doses were equal to 5.4 mSv and 6.3 mSv using AEC and without using AEC, respectively. Maximum organ effective doses were 15, 14, 14 and 14 mSv for breast, esophagus, lung and thymus respectively in the non-using AEC system imaging technique.
Conclusion: Our measurements indicated a decrease about 15% in weighted CT dose index (from 12.46 to 9.94 mGy) using AEC system. Beside of this fact, the noise increased about 11.3% (from 4.2 to 4.74) using AEC system. So, it can be said that using of AEC was an effective way for dose reduction in women undergoing chest CT scanning, and the additional noise was in the acceptable range.

Amin Banaei, Bijan Hashemi, Mohsen Bakhshandeh, Bahram Mofid,
Volume 77, Issue 2 (May 2019)
Abstract

Background: Intensity-modulated radiotherapy (IMRT) is one of the most usable methods in prostate radiotherapy that is used with different techniques. The aim of this study was to evaluate and compare the dosimetric and radiobiological effects of prostate IMRT techniques regarding to joint volume between the target tissue and organs at risk as a patients anatomical parameter.
Methods: This research was a cross-sectional, analytical, and quantitative study that was carried out from April 2016 to June 2018 at the radiotherapy and oncology center of Shoheday-e-Tajrish Hospital and Medical Physics Department of Tarbiat Modarres University Tehran, Iran. Four various prostate IMRT techniques (9, 7 and 5 fields and automatic) were planned on 63 prostate cancer patients CT scans. Radiobiological effects were calculated using Relative Seriality model for the organs at risk (bladder and rectum) and target tissue. Results of mentioned prostate IMRT techniques were compared based on the patient’s anatomical parameter. 
Results: For the patients with joint volumes ranged from 0 to 15%, statistical differences were not observed among various IMRT techniques. The tumor control probability and complication free tumor control probability values decreased as a function of joint volume. The normal tissue complication probability value increased as a function of joint volume. The 9 and 7 fields IMRT techniques had not any significant differences (P=0.06) in all of the joint volume ranges. In patients with the joint volumes higher than 30%, the 9 and 7 fields techniques showed significantly better radiobiological values in comparison with 5 fields and automatic techniques (P=0.009).
Conclusion: In the patients with lower percentage of joint volume, all the mentioned prostate IMRT techniques showed same radiobiological effects; however, in the patients with higher joint volume percentages (> 30%), the 9 and 7 fields techniques have better results. It is proposed to use the 7 fields technique instead of the 9 fields technique, especially in prostate cancer cases with high uncertainty in patients’ setup.


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